Pressure sensor apparatus and transducer therefor

ABSTRACT

A transmitter for receiving two fluid inlet pressures from opposite sides of an orifice in a pipeline or otherwise to produce a D.C. output current from, for example, 4 to 20 milliamperes directly proportional to the difference between the inlet pressures. The output of the transmitter may be connected to a milliammeter calibrated in pressure (pressure difference) or to a process controller or otherwise. The transmitter includes a differential pressure unit that, in turn, includes two pressure sensors or diaphragms connected in tandem. Diaphragm movement is converted to strain in a strain gage transducer that has two strain gages that are connected in a Wheatstone bridge with other resistors in the transmitter circuit. The transmitter circuit provides the said output current and may be conventional. Wheel embossed diaphragms operate with an extremely low maximum nonlinearity for large deflections considering their low rate. For example, the rate is equivalent to a flat diaphragm but has a linear deflection ten times that of a flat diaphragm. Also, the rate is one-tenth the rate of a conventional corrugated diaphragm at equal or improved linearities in the range of deflections desirable. The differential pressure unit also has two flat back plates in which the respective diaphragms can stop when overpressure protection is needed. Therefore, no close fitting contours or valve operated liquid stops are required. The speed of response of the transmitter is kept advantageously high by employing limited full scale deflection. This deflection may be, for example, 0.015 inch for a 1.75 inches effective diameter. BACKGROUND OF THE INVENTION SUMMARY OF THE INVENTION

United States Patent 11 1 Garnett et a1.

1 1 PRESSURE SENSOR APPARATUS AND TRANSDUCER THEREFOR [75] Inventors:Lawrence Taylor Garnett, Fullerton;

Laverne Dean Lyon. Claremont. both of Calif.

[73] Assignee: International Telephone and Telegraph Corporation, NewYork, NY.

22 Filed: on. 1, 1973 [21] App1.No.:402,361

[52] US. Cl. 73/398 AR; 73/407 R; 92/97; 92/104 [511 int. Cl. G011 9/04[58] Field of Searchm 73/407, 398 AR. 408. 393. 73/397. 406'. 92/97.104. 130. 131. 133. l.

[56] References Cited UNITED STATES PATENTS 2.174.171 9/1939 Wasson eta1 148/123 3.079.953 3/1963 Mounteer 92/104 3.389.362 6/1968 McLellan3.500.271 3/1970 Strauch 3.720.108 3/1973 Freitag 73/407 R 1 1 Apr. 8,1975 Primary E.\'tlllll7l(fHClhEl'i Goldstein Ass/sum! E.raniiner-MarcusS. Rasco Attorney. Agent. or Firm-A. Donald Stolzy [57] ABSTRACT Atransmitter for receiving two fluid inlet pressures from opposite sidesof an orifice in a pipeline or otherwise to produce a DC. output currentfrom. for example. 4 to 20 milliamperes directly proportional to thedifference between the inlet pressures. The output of the transmittermay be connected to a milliammeter calibrated in pressure (pressuredifference) or to a process controller or otherwise. The transmitterincludes a differential pressure unit that, in turn. includes twopressure sensors or diaphragms connected in tandem. Diaphragm movementis converted to strain in a strain gage transducer that has two straingages that are connected in a Wheatstone bridge with other resistors inthe transmitter circuit. The transmit ter circuit provides the saidoutput current and may be conventional. Wheel embossed diaphragmsoperate with an extremely low maximum non-linearity for largedeflections considering their low rate. For example. the rate isequivalent to a flat diaphragm but has a linear deflection ten timesthat of a flat diaphragm. Also, the rate is one-tenth the rate of aconventional corrugated diaphragm at equal or improved linearities inthe range of deflections desirable. The differential pressure unit alsohas two flat back plates in which the respective diaphragms can stopwhen overpressure protection is needed. Therefore. no close fittingcontours or valve operated liquid stops are required. The speed ofresponse of the transmitter is kept advantageously high by employinglimited full scale deflection. This deflection may be, for example.0.015 inch for a 1.75 inches effective diameter.

14 Claims. 16 Drawing Figures 7/ 7 as I we PATENTEDAPR 81975 SELET 1 BF5 D/FFER EN T/QL PEESSU/Q E 46k. C/N/T TQANSM 7' TE 2 (JT/L IZAT/OA/MEANS FIGZJ.

NTEIHEDAPR 8 19. 5

SHEET 5 BF 5 FIG.I6.

Awqqum 331 k0 kwuqw w DEF L EC 77 ON (INCH PER INCH OF DIAMETER)PRESSURE SENSOR APPARATUS AND TRANSDUCER THEREFOR BACKGROUND OF THEINVENTION This invention relates to pressure sensors, and moreparticularly, to apparatus for producing an output which is a functionof one or more pressures of one or more fluids.

In the prior art, it has been the practice to connect two chambers ofadevice known as a differential pressure unit (DPU) to a pipeline onopposite sides of an orifice therein. The DPU is a part of apparatuscommonly called a transmitter. The output of the transmitter is thenimpressed upon a DC. milliammeter, a process controller or otherwise. Ifdesired, the milliammeter may be calibrated to read directly in pressureor differential pressure. Alternatively, the milliammeter may becalibrated to read directly in volume rate of flow. For example, themilliammeter may be calibrated to read in cubic feet per minute.

The most popular DPU in the past seems to have been of the doublebellows type. For example, see U.S. Pat. Nos. 2,590,324; 2,917,08l',2,945,5 l and 3,343,420. However, metal diaphragm DPUs are not unknown.See U.S. Pat. Nos. 3,492,872 and 3,620,135. Metal diaphragms are alsoknown in non-analogous arts. See U.S. Pat. Nos. I92] ,321; 2,913,008and3,079,953. Metal diaphragms are preferred because of superior cleaningcapability.

Prior art transmitters operate with l high maximum non-linearization,(2) short ranges, or (3) diaphragm high minimum range with expensive orno overpressure protection. The diaphragms and bellows of the DPU'sthereof also have low intrinsic rupture strengths. For example. atypical prior art DPU uses two complicated overpressure valves foroverpressure protection.

SUMMARY OF THE INVENTION In accordance with the pressure sensorapparatus of the present invention, the above-described and otherdisadvantages of the prior art are overcome by providing pressure sensorapparatus which has a high linearity over a very large range at a lowrate with high intrinsic resistance to overpressure.

One outstanding feature of the present invention resides in the use ofan embossed wheel pattern on a diaphragm, this construction providinggood linearity over a long range at a low spring rate. The embossedwheel pattern diaphragms also have an exceedingly high rupture strengthresulting in the use of inexpensive noncontoured back plates on which adiaphragm is supported for over pressure protection.

The above-described and other advantages of the present invention willbe better understood from the following detailed description whenconsidered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings which are to beregarded as merely illustrative:

FIG. 1 is a schematic diagram of one embodiment of the presentinvention;

FIG. 2 is a top plan view ofa differential pressure unit (DPU)constructed in accordance with the present invention;

FIG. 3 is a left end elevational view of the DPU shown in FIG. 2;

FIG. 4 is an end elevational view ofa cover plate, two

of which are employed in the DPU of FIGS. 2 and 3;

FIG. 5 is a top plan view of the cover plate shown in FIG. 4;

FIG. 6 is a longitudinal sectional view through the cover plate taken onthe line 66 shown in FIG. 5;

FIG. 7 is a vertical sectional view of the DPU taken on the line 7-7shown in FIG. 2;

FIG. 8 is a top plan view of a strain gage assembly employed in the DPUof FIGS. 2 and 3;

FIG. 9 is a vertical sectional view taken on the line 9-9 of the straingage assembly shown in FIG. 8;

FIG. 10 is a perspective view of a metal stamping shown in FIGS. 8 and9;

FIG. 11 is a vertical sectional view taken on the line 11-11 of the DPUshown in FIG. 2;

FIG. 12 is an end elevational view also shown in FIG. I1;

FIG. 13 is a top plan view ofa diaphragm constructed in accordance withthe present invention;

FIG. 14 is a greatly enlarged radial sectional view taken on the linel4l4 of the diaphragm shown in FIG. 13;

FIG. 15 is a vertical sectional view through the diaphragm shown in FIG.13 and taken on the line 15-15 therein; and

FIG. 16 is a graph of the linearity or non-linearity characteristics ofthe diaphragm shown in FIG. 13 and a conventional corregated diaphragm.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings, in FIG. 1, apipeline is illustrated at 40 having a disc 41 sealed therein, disc 41having an orifice 42. Conduits 43 and 44 are connected from pipeline 40on opposite sides of orifice 42 to a differential pressure unit 45. Atransmitter circuit 46 is connected from the output of differentialpressure unit 45 (DPU 45) to utilization means 47.

DPU 45 and circuit 46 together form what is commonly known as atransmitter. Utilization means 47 may be a milliammeter calibrated indifferential pressure or in volume rate of flow. Alternatively,utilization means 47 may be a process controller or otherwise.

DPU 45 is illustrated in FIGS. 2I5, inclusive.

Transmitter circuit 46 may be any conventional transmitter circuit.Alternatively, transmitter circuit 46 may be identical to that disclosedin U.S. Pat. No. 3,518,886, the two strain gages disclosed hereinafterbeing substituted for those two strain gages disclosed in the said U.S.Pat. No. 3,518,886. Some of the structures disclosed in U.S. Pat. No.3,5l8,886 are duplicated in FIGS. 8 and 9 hereof. Thus, where suchstructures are duplicated, those structures may be omitted from theportion of the structures which are disclosed in U.S. Pat. No. 3,518,886when the structures not omitted are incorporated in the transmittercircuit 46.

It may be of assistance to note that throughout the FIGS. 2-15,inclusive, some of the several views are drawn to one scale and othersto other different from the said one scale. Some views have beenenlarged or greatly enlarged for clarity. Some background lines havealso been omitted in connection with the diaphragms shown in FIGS. ll,13 and 15, for clarity.

In FIG. 2, the DPU is indicated again at 45. DPU 45 has two coverplates. One cover plate is illustrated at 48 in FIG. 2. The other coverplate cannot be seen in FIG. 2 because it is exactly the same size ascover plate 48 and is aligned therewith. The other cover plate isillustrated at 49 in FIG. 3. Cover plate 49 will not be de scribed indetail because it is identical to cover plate 48.

In FIG. 2. cover plate 48 has an upwardly extending boss 50. Both co\ erplates 48 and 49 are clamped over a body 51 shown in FIG. 3 by bolts 52,53 and 54. shown in FIG. 2.

In FIG. 2. DPU includes a hollow cylindrical tube 55 fixed relative tobody 51. Tube 55 provides a boil ing for electrical leads which may beconnected with the DPU 45. Tube 55 is illustrated in FIGS. 8 and 9 on alarger scale.

In FIG. 3. it will be noted that bolt 53 has a head 56 which abuts ancar 57 on cover plate 48. Bolt 53 has a shank 58 which is threaded at59. A nut 60 is threaded to shank 58 and pulls cover plates 48 and 49together firmly locking and clamping body 5] in a fixed positionrelative to the cover plates 48 and 49.

(over plate 49 has an car 61. A lock washer 62 is provided around boltshcnk 58 between nut 60 and ear 61. (over plate ears 57 and 6t haveholes therethrough through which bolt shank 58 projects. All the bolts52. 53 and 54 are. more or less. symmetrically positioned and have thesame construction. are provided with nuts and lock washers. and help tohold the co er plates 48 and 49 in clamping engagement with body 5 inexactly the same way that bolt 53 does and as illustrated in FIG. 3 anddescribed in connection with the showing in FIG. 3.

In FIG. 3. each of the cover plates 48 and 49 have end faces 63 and 64.respectively. As will be explained. cover plate 48 forms a first sealedchamber with body SI. Similarly. cover plate 49 forms a second sealedchamber with body 5] different from the said sealed chamber. In FIGS. 4and 5. cover plate 48. thus. has a port 65 thercthrough into the saidfirst sealed chamber. End face 63 of cover plate 48 in FIGS. 3 and 4 hasa counterbore at 66. End lace 63 of cover plate 48 also has tapped holes67 and 68 therein. The construction of port 65. counterbore 66 andtapped holes 67 and 68 is merely to provide a fluid coupling to. forexample. any conventional conduit and end fitting therefor such as maybe employed with conduits 43 and 44. In one example. the conduit itselfmay have a grooved end sur face and an ()-ring in the groove to sealagainst the annular end surface 66' of counterbore 66 and the port 65.See FIG. 4. Cap screws then may be employed to hold the fitting by beingthreaded into tapped holes 67 and 68.

FIG. 4 is a view otcover plate 48 turned 90 from the position shown inFIG. 3.

FIG. 5 is another top plan view of cover plate 48 illus trating the boltholes 69, 70 and H through ears 72, 57 and 73 thereof. respectively.

In FIG. 5. cover plate 48 is cup shaped and has a cup shaped chamber orrecess 74 therein with which port 65 lies in communication. See FIG. 6.

In FIG. 7. a portion of a strain gage assembly 75 is illustrated fixedrelative to body 51 by four hex head screws 76 that are slidable throughcorresponding holes in a flange 77 and are provided with washers 78.Flange 77 is illustrated both in FIGS. 8 and 9. However. the tappedholes in body 51 into which screws are threaded and the holes throughflange 77 through which screws 76 are slidable are not illustrated.

(ill

As shown in all of the FIGS. 7. 8 and 9 flange 77 is provided with anannular boss 79. Tube 55 is brazed or otherwise fixed to tlangc boss 79at 80 as shown in FIG. 9. Tube 55 is also illustrated in FIG. 7.

Four electrical conductors extend from the interior of body 51 to theexterior thereof. although only two such conductors. ie. conductors 81and 82, are illustrated in FIG. 9.

All four of the conductors are sealed through a glass disc 83. Glassdisc 83 is. in turn. sealed within a metal ring 84. Metal ring 84 is. inturn. fixed in a bore 85 of a square tube 86 which is integral withflange 77.

Flange 77 has an O-ring groove 87 therein in which an O-ring 88 islocated. Thus. when screws 76 draw flange 77 tight to body 51. a fluidtight seal is provided around an opening 89 through the wall of body 51.The reason for this is the DPU 45, as well as some conven tional DPUsare filled with a liquid. In the instant case. the liquid fills theentire interior of body 51. At least as the space inside thereof isdefined thereby and surrounding structures including. but not limitedto. two diaphragms will be described.

In the construction illustrated in FIG. 9. a block or square rod section90 is slidably positioned at the loca tion illustrated in FIG. 9. Ilody90 has a hole 91 extend ing part way lhcreinto. Tube 86 also has a hole92 which is aligned with body hole 91. A locator pin 93 is then placedthrough both ol the holes 91 and 92. Pin 93 may be press lit in eitherone or both of the tube 86 and the body 90.

A Ieat spring cantil ever beam 94 and a clamping plate 95 have holeswhich may be approximately aligned with a screw hole 96 through tube 86and hold 92 into tube 86. Beam 94 and plate 95 may then be put in theposition shown in FIGS. 8 and 9. and screw 97 slidably positionedtherethrough and screwed into body 90 down tight against plate 95.

Beam 94 and some of the other structures illustrated in FIGSv S and 9.to the right of line 98 in FIG. 8. may be entirely conventional. Forexample. it is conventional to bond a strain gage at the same locationon opposite sides of beam 94. Both such strain gages are emloyed. Onlyone such strain gage is illustrated at 99 in FIG. 8.

As is well known. each strain gage has two leads. Thus. one lead of eachstrain gage is connected to a corresponding respecti e conductor. Theother leads of the strain gages are then connected to the respectiveconductors 81 and 82. An electrical lead IOU is connected from one endof strain gage 99 in FIG. 9. Another electrical lead 101 is ct'innectedfrom the other end of the strain gage 99. The connection of leads andI01. and the two leads from the other strain gage to the conductors suchas conductors 81 and 82. have been omitted for clarity.

A metal stamping 182 illustrated in FIG. 8 has a tab l03 that is brazedor otherwise tired over its entire area to an end portion 104 of beam94. See also FIGS. 9. and 10.

In FIG. 9. beam 94 has a portion 105 and a portion 106. Portion 106 isthe ti ted end portion. Portion 104 is the free end portion. Portion I05is tapered as shown in FIG. 8. Portion 105 is called the constant strainregion and is conventional. Portion I06 is also eonventional Portion I04is not conventional Portions 104 and I05 are integral with one another.Similarly. portions 105 and 106 are integral with one another. A topplan view of portion 106 would be identical to a top plan view of plate95 in a view similar to that shown in FIG. 8.

As shown in FIG. 10. stamping 102 is made by shear ing an aperture 107therein which is somewhat U- shaped leaving tab 103. which is struckout, in a plane approximately perpendicular to the plane of theremainder of the stamping 102.

An enlarged sectional view of the DPU 45 taken on the line l1ll in FIG.2 is shown in FIG. 11.

In FIG. 11, body 51 is illustrated including a block 108 having plates1'09 and 110 fixed against opposite annular end faces 117 and 118,respectively, of the block 108, block 108 having a cylindrical externalsur face 111 which may or may not be occasionally interrupted by otherstructures. Plates 109 and 110 are generally cylindrical but have endflanges 112 and 113, respectively.

Plate 109 is held tight against block 108 by a ring 114 that has aflange 115 to overlie flange 112. Preferably, four screws 16 areslidable through ring 114 and threaded into block 108 to hold plate 109tight to block 108.

Cover plates 48 and 49 are again shown in FIG. 11. Ring 114 has anO-ring grove 119 therein. An O-ring 121 is located in groove 119 of ring114. O-ring 121 provides a fluid tight seal between cover plate 48 andplate 109.

All the structures shown above the block end face 117. as viewed in FIG.11, may be identical to all the structures shown below the block endface 118. For this reason, only a portion of the structures shown belowblock end face 118 will be described in further detail.

In FIG. 11. a generally circular metal diaphragm 123 is illustratedhaving an annular portion 124 which is seam welded to plate 109 on anannular surface 125 thereof. The seam weld provides a fluid tight sealaround the complete circumference of plate 109 and also fixes theannular portion 124 of diaphragm 123 in position relative to plate 109.

In FIG. 11, diaphragm 123 has a circular center por tion 126 to which adisc 127 is everywhere bonded. Disc 127 may have a stud 128 integraltherewith or otherwise fixed thereto that is threaded into a tapped hole129 in one end of a center post 130.

Plate 110 similarly has a metal diaphragm 131 fixed thereto. Inaccordance with the foregoing, both of the diaphragms 123 and 131 arefixed relative to the ends of post 130.

Post 130 preferably is slidable through certain bores in block 108.Preferably the diameters of the bores are oversize so that the post 130does not touch any of them.

Note will be taken, in FIG. 11. that cover plate 48 and diaphragm 123are spaced apart and define a chamber 132 therebetween, as mentionedpreviously. Similarly, cover plate 49 and diaphragm 131 define a chamber133. Chambers 132 and 133 are fluid tight. For example, chamber 132 isfluid tight because of the use of O-ring 121, and also because the seamweld provides a seal between the annular portion 124 of diaphragm 123and the annular surface 125 of plate 109.

The chambers 132 and 133 are fluid tight except, of course, for port 65in cover plate 48 shown in FIG. 6 and a port identical to port 65 incover plate 49.

Block end face 117 has an O-ring groove 134 therein in which an O-ring135 is positioned to provide a fluid tight seal between block 108 andplate 109. Similarly, an O-ring groove 135 is provided in end face 118,and an O-ring 137 is positioned therein to provide a fluid tight sealbetween block 108 and plate 110.

Annular filler blocks 138 and 139 are provided to minimize the amount offluid needed to fill all communicating chambers between the diaphragms123 and 131, inside thereof. It is conventional. for example. to fill abellows-type differential pressure unit with a silicone oil or otherliquid as a partial overpressure protection.

A helically coiled spring 140 is provided having one end 141 fixed toblock 108 and another end 142 fixed to a flange 143 which may be fixedto or integral with post 130.

Spring 140 may be omitted in some cases. When spring 140 is omitted, theDPU 45 becomes bi directional. That is, the pressure in chamber 132 maybe higher than that in chamber 133 or the pressure in chamber 133 may behigher than that in chamber 132. As shown, chamber 133 is the highpressure chamber. This is true because the force applied to flange 143by spring 140 is in opposition to the deflection taken by diaphragm 131on account of an increase in pressure in chamber 133.

In FIG. 11, stamping 102 is clamped to flange 143 in a fixed positionrelative to post 130 by a clamping plate 144 that holds stamping 102tight against flange 143. plate 144 being held in a clamping position onstamping 102 by hex head screws 145 and 146 threaded into flange 143.Screws 145 and 146 thus hold plate 144 tightly against stamping 102,and, in turn, stamping 102 tightly against flange 143.

Portions 123' and 131' of diaphragms 123 and 131 nest in plates 109 and110 during respective overpres sures. When so nesting. diaphragmportions 123' and 131' seat upon respective frusto-conical surfaces 109'and 110' of plates 109 and 110, respectively.

As shown in FIGS. 11 and 12, plate 144 is U-Shaped.

Flange 143, as shown in FIG. 12, has a step portion 147. Flange 143 alsohas bleed holes 148 and 149. Bleed holes 148 and 149 extend completelythrough flange 143 and allow fluid on opposite sides of the flange 143to flow therethrough more easily to increase the speed of response ofthe DPU 45, if desired. Alternatively, or in addition, bleed holes 148and 149 may provide moderate or large restrictions to flow and therebyoperate to damp the output of DPU 45.

As stated previously, diaphragm 131 may be identical to diaphragm 123,if desired. Diaphragm 123 will, thus, be the only diaphragm which willbe described in further detail.

FIG. 13 is a top plan view of the diaphragm 123. If desired. diaphragm123 may have a substantially uniform thickness throughout its completeextent. Dia phragm 123 is preferably made by forming a circular, thin,flat blank of uniform thickness equal to about 5 mils of l7-7 or [7-4precipitation hardenable stainless steel. However, other materials arepossibleeven plastic. However, the said precipitation hardenablestainless steel is preferable for rupture strength. Other materialswhich may be used are Martensitic stainless steel, 400 stainless steel,the cobalt alloys such as the Hamilton Watch Companys cobalt alloy soldunder the trade name Elgilloy." Alternatively, 316 stainless steel maybe employed. Diaphragm 123 maybe made of any formable material having aductility of 25 percent or more.

Diaphragms 123 and 131 may be made in an identi cal manner, ifdesired.Diaphragm 123 is, thus, formed between dies in a press to the size andshape illustrated, although not necessarily to scale, in FIGS. 13, 14and 15.

In FIG. 13, diaphragm 123 is shown with the annular portion 124 thereof.Annular portion 124 may have substantially flat parallel surfaces inrespective parallel planes except for a cylindrical surface 150 over thethickness thereof. Diaphragm 123 then has portions 151 and 152 whichhave opposite surfaces, each of which would generally be defined asone-half of a torus cut by a plane normal to the axis thereof withradii, R and r, defining different torus locations of certain surfacesof the portions 151 and 152.

The axis ofthe torus which would define one surface of portion 152 wouldbe generally identical to the axis of the torus which would define onesurface of portion 151. This axis would lie perpendicular to the planeof the drawing of FIG. l3 through the point 153. The portions 151 and152 are connected by spokes 155, which with portions 151 and 152, forman embossed wheel 154. Each pair of immediately adjacent spokes 155 isconnected by arcuately shaped webs 156. Each web also connects portions151 and 152.

Each web 156, when diaphragm 123 is unstressed, has an upper surfacethat lies generally in the same plane as the upper surface of annularportion 124 and the upper surface of portion 126. The lower surfaces ofportions 156, 124 and 126 similarly lie in the same plane.

Spokes 155 have generally a half cylinder shape. They may, for example,have a diameter, F, equal to about I30 mils, as shown in FIG. 15. Thedimension, E, shown in FIG. 13 may also be I30 mils, if desired. Thesame is true of the dimension, D.

In FIG. 13, the dimention, G, may be ll5 mils. if desired.

A view of the diaphragm 123 on the reverse side thereof might besubstantially identical to that shown in FIG. 13. However, in this case,the cmbossments would become channels. Note that the diaphragm 123 hasthe spokes 15S and the portions 151 and 152 which are embossments on oneside, i.e. on the side shown in FIG. 13. Thus, on the reverse side, theembossrnents become channels because diaphragm 123 has a substantiallyuniform thickness. In such a case, each channel corresponding to onespoke 155 would then lie in communication with channels in correspondingportions 151 and 152 as indicated by arrows 157 in FIG. 13.

lfdesired, the radius, R, may equal 21/2 inches. The radius, r. may be.if desired, one/half inch.

In FIG. 14, preferably portion 151 has a curvature, as shown, which isas nearly accurate to a semi-circle as possible. However, it may be asomewhat more complicated arc. The same would be true of a correspondingradially extending section through portion 152 and a section through 3spoke 155 normal thereto.

As stated previously, background lines have been omitted in connectionwith the diaphragms 123 and 131 in FIGS. 11, 13 and 15 in several placesfor clarity. For example, background lines have been omitted at 158 infour locations in FIG. 15.

OPERATION If fluid under pressure is admitted to chamber 133, which hasa pressure in excess of the pressure of fluid in chamber 132, diaphragms123 and 131 will deflect upwardly, as viewed in FIG. 11, moving post 130in the same direction. Stamping 102 is fixed to post 130 and, therefore,deflects beam 94 shown in FIG. 8 in a downward direction in FIG. 9because of the view takenv Strain will then be induced in both of thestrain gages fixed to beam 94, and transmitter circuit 46 connected fromthe strain gages may cause utilization means 47 to indicate volume rateof flow, for example. As stated previously, utilization means 47, inthis case, may be a milliammeter calibrated in volume rate of flow orgallons per minute. The ouput of transmitter circuit 46 in FIG. 1 maythenvbe a DC. current directly proportional to the difference betweenthe pressures of the fluids in chambers 133 and 132.

One outstanding advantage of the DPU 45 is its linearity. This linearityis plotted at 159 in FIG. 16 as a function of deflection. The linearityofa corrugated circular diaphragm is plotted at 160 in FIG. 16 from datapublished by the US National Bureau of Standards. In FIG. 16, note willbe taken that curve 159 has a portion 161 over a deflection range whichhas a substantially better linearity than the curve 160. It is, in fact,gener ally in this area ofcurve 159 which the diaphragms 123 and 131 areoperated.

Actually, it is common to call the curves 159 and 160 "linearity"curves. The fact of the matter is that the function graphed is afunction of non-linearity rather than linearity. A point such as the Xmarked point 162 is taken from performance data. A pressure versusdeflection curve is plotted first. The non-linearity, for ex ample, atpoint 162 is then calculated by drawing a straight line from the origin(0, 0) to a point on the pressure versus deflection curve. The maximumerror between Zero and, for example, point 162 is measured. The percentlinearity (actually non linearity) for point 162 is then calculated bydividing the maximum error by the ordinate of point 162 and multiplyingtimes [00.

By use of the embossed wheel pattern 154, it is possi ble to obtain goodlinearity over a large deflection, and to obtain a large deflection overa small pressure range.

The phrase means to supply fluid under pressure is hereby defined foruse herein and in the claims to mean any one or more or all of thefollowing, with or without other structures: a source of fluid underpressure, a conduit, a port or a similar admitting orifice.

The word output, as used herein and in the claims, is hereby defined toinclude an output which is either mechanical or electrical or otherwise.

The word *integral is hereby defined for use herein and in the claims toexclude a bolted, screwed, bonded, sealed or other connection of partsfastened together in any other similar ways. but to include only amolded or formed single, unitary piece of material that is found thatway in its natural state or has been produced by a chemical reaction orsmelted or the like such that it is substantially isotropic throughout aconnection of two parts.

The phrase utilization means is hereby defined for use herein and in theclaims to include, but not be limited to, an ammeter or milliammetercalibrated in vol ume rate of flow or in differential pressure, aprocess controller or otherwise.

In FIG. 16, curve 160 has points 164, 165 and 166. The data for all thepoints 161 to 166, inclusive, are as follows. The diaphragmscorresponding to the curves 159 and 160 in FIG. 16 each had a radius, R,equal to 0.875 inches. The deflections for points 164, 165 and 166 wererespectively equal to one/half, l and 2 percent of 2R. Points 164, 165and 166 had percent nonlinearities of 0.8, 0.7 and 0.4, respectively.For the same one/half, l and 2 percent of 2R deflections, points 163.162 and 161 had percent nonlinearities of 0.l, 0.6 and 2.6,respectively.

After diaphragm 123 in FIG. 13 is formed as shown therein and as shownin FIGS. 14 and 15, diaphragm 123 is precipitation hardened. This may bedone by any conventional method. For example, diaphragm 123 may beheated in an evacuated chamber to l,550F. and the l,550F. held for 90minutes. The diaphragm 123 is then cooled to room temperature by turningoff the heat to the vacuum chamber and by passing nitrogen or anothergas or gas mixture providing a neutral atmosphere through the vacuumchamber at about one atmosphere. Preferably, the diaphragm 123 is cooledto room temperature within one hour immediately succeeding the 90 minuteperiod described above in this paragraph. Diaphragm 123 is thenrefrigerated to F. for minutes. Diaphragm 123 is then heated in thevacuum chamber again to l,050F. and this l,050F. temperature held for 90minutes. The diaphragm 123 is then cooled in the same manner as before.

In an alternative embodiment of the invention, diaphragms may be coatedwith layers of plastic 2 or 3 mils thick for corrosion resistance orotherwise.

In the prior art, two openings have sometimes been employed into theinterior of a DPU. These openings are employed so that air may beevacuated through one opening, and the fluid to fill the interior of theDPU may be introduced through the other opening. Such openings are notdisclosed herein but any conventional ports may be provided for thatpurpose.

In FIG. 13, the curvature of the portions 151 and 152, and the curvatureof the spokes 155 are specially adapted to make the diaphragm 123strong. It will withstand exceedingly high loads.

Any conventional transducer may be substituted for the portion of atransducer shown in FIG. 8. Alternatively, the strain gages in FIG. 8may be bonded to beam 94 by the use of glass, an epoxy or otherwise. Asalternatives for the transducer of FIG. 8, a torque tube output or anelectromechanical pick-up or other devices are also possible.

Diaphragms 123 and 131 may alternatively be made of 316 stainless steel.

Notwithstanding the foregoing, it will be appreciated that the use oftwo diaphragms is not always required. The present invention may bepracticed by the use of one diaphragm. For prior art on single bellowsand differential pressure units. see, for example US Pat. No. 2,752,949.

As stated previously. the large bonding areas and flexibility of the tab103 of stamping 102 and its bond over its entire area to the portion 104of beam 94 in FIG. 8 provide for extremely good accuracy.

The phrase full scale deflection" is hereby defined to includedeflection in one direction only either away from or toward anunstressed position.

This application contains some subject matter common to that disclosedin applications Ser. Nos.

402,336; 402,036; and 402,035, all filed on Oct. I, I973, by L. T.Garnett, R. P. Granada and L. D. Lyon, respectively, for MECHANICAL SPANAND ZERO ADJUSTMENT APPARATUS FOR PRESSURE TRANSMITTERS, COLD WORKINGPROCESS AND FLUID PRESSURE SENSING SYSTEM AND DIFFERENTIAL PRESSURE UNITTHEREFOR, respectively.

In FIG. 16, the diaphragm of curve has an equally bad linearity whendeflected in the opposite direction and an undesirable abrupt change inrate at a neutral (eg. zero deflection) position. The diaphragm ofthecurve 159 had an equally good linearity when deflected in the oppositedirection (one-half of non linearity indicated in FIG. 16) and noundesirable abrupt change in rate at a neutral position. In these twoinstances, rate" means the slope of the curves 159 and 160 on oppositesides of the neutral position at small positive and negativedeflections, e.g. at deflections of 0008 inch, more or less.

The tapped hole 68 in FIG. 5 has been omitted in FIG. 11 for clarity.

What is claimed is:

1. Apparatus for connection from a source of a fluid under pressure toproduce an output which is a function of the fluid pressure, saidapparatus comprising: a body having a hole extending completelytherethrough; a generally planar, flexible diaphragm fixed relative tosaid body over each end of said hole, each said diaphragm having acentral portion including a circular embossment outside said body havinga surface the same as one-half ofa torus cut by a plane normal to itsaxis, each said diaphragm having an approximately uniform thicknessthroughout its extent, each of said diaphragm central portions alsoincluding a circular flat portion everywhere connected with saidembossment inside thereof; a disc for each diaphragm of approximatelythe same diameter as those of the respective di aphragm flat portionsand everywhere bonded thereto, each said disc having a threaded stud onthe same axis; a post threaded at its opposite ends to said studs,respectively, said post being fixed relative to both of said studs;input means for supplying fluids to one side of each of said diaphragmsoutside said body, said fluids being under different pressures; andoutput means connected between said post and said body to produce anoutput which is a function of the difference between the pressures ofsaid fluids.

2. A transducer comprising: a base; a member; means mounting said memberon said base to move in a predetermined direction in accordance with apredetermined variable; a leaf spring cantilever beam having a beamplane and a plane of symmetry normal thereto and having one fixed endand another opposite end free; a strain gage fixed to opposite sides ofsaid beam; means mounting said beam in a fixed position relative to saidbase and in a position approximately normal to said predetermineddirection; a stamping fixed to said memher to move generally in a planenormal to both of said symmetrical and beam planes, said stamping havinga U-shaped hole punched therethrough leaving a tab thin in comparison toits length which is struck out into a plane which is generally normal tothat of said stamping, said beam free end projecting toward said holeover and being fixed relative to said tab in a position spaced from saidstamping plane; and output means connected from said strain gages toproduce an output signal of a magnitude directly proportional to saidmember movement.

3. The invention as defined in claim 2. wherein said mounting meansincludes means to move said member in a manner to cause said beam tobend only in said predetermined direction.

4. Apparatus for connection from a source of a fluid under pressure toproduce an output which is a function ofthe fluid pressure. saidapparatus comprising: an annular body having a flat. annular surfacebetween a first inner circle and a first outer circle concentric withsaid first inner circle; a generally planar circular diaphragm having agenerally symmetrical center and an axis through said center normal tothe diaphragm plane. said diaphragm also having a flat circular portionaround said center and a flat annular portion at its outer edge betweena second inner circle and a second outer circle concentric with saidsecond inner circle. said diaphragm annular portion being fixed relativeto said body annular surface in a position such that all of said circlesare concentric with said diaphragm axis. said second outer circle havinga predetermined diameter. said diaphragm having an approximately uniformthickness throughout its extent. which thickness is substantially lessthan said second outer circle diameter, said diaphragm having anintermediate portion con nected between said circular and annularportions thereof. said diaphragm intermediate portion having awheel-shaped embossment thereon. said wheel having a hub portion. a rimportion and a plurality of spokes. said hub portion being connected fromsaid diaphragm circular portion to said spokes. said hub portion havinga surface in the shape of one-half of a first torus cut by a planenormal to its axis. said first torus axis being con gruent with saiddiaphragm axis, said rim portion being connected from said spokes tosaid diaphragm annular portion. said rim portion being spaced radiallyfrom said hub and having a surface in the shape of one-balf of a secondtorus cut by a plane normal to its axis. said second torus axis alsobeing congruent with said diaphragm axis. said hub portion. said rimportion and said spokes all being embossed on the same side of said diaphragm intermediate portion. said hub portion. said rim portion and saidspokes all being concavo-convex and defining respective channels in theother side of said diaphragm due to the approximately uniform thicknesstherof. the channel ofeach spoke communieating with both of those ofsaid hub and rim portions. said diaphragm intermediate portion having aflat arcuate portion filling the gap between and connected be tween eachpair of immediately adjacent spokes and filling the gap between andconnected between the re spective hub and rim portions connecting eachsaid respective pair of immediately adjacent spokes. said spokes beinguniformly distributed around and projecting in radial directions frontsaid diaphragm axis. the surface of each said flat portion on said onediaphragm side lying generally in a single plane when said diaphragm isunstressed; input means for supplying a fluid under pressure to said oneside of said diaphragm; and output means including auxiliary meansconnected between said diaphragm circular portion and said body toproduce an output which is a function of said fluid pressure.

5. The invention as defined in claim 4, wherein each of said spokesapproximately has the shape of a thin hollow half cylinder ofapproximately concentric internal and external surfaces which areuniform in diameter throughout the length of each respective spoke. allof said internal spoke surface diameters being the same. all of saidexternal spoke surface diameters being the same. each half cylinderbeing formed by cutting a thin hollow cylinder with a plane through thecylinder axis.

6. The invention as defined in claim 5, wherein said output meansincludes utilization means connected from said auxiliary means.

7. The invention defined in claim 6, wherein said auxiliary meansproduces a DC. current directly proportional to said fluid pressure.said utilization means including a milliammeter calibrated in weight perunit area.

8. The invention as defined in claim 7. wherein said diaphragm is madeof metal. said spokes being eight in number. each immediately adjacentpair of spokes having radial axes angularly spaced apart 45, saiddiaphragm annular portion being sealed to. fixed to and bonded to thecomplete circumference of said body annular surface by being seam weldedthereto.

9. The invention as defined in claim 5. wherein said diaphragm is madeof metal.

10. The invention as defined in claim 4, wherein said diaphragm is madeof metal.

11. The invention as defined in claim 5, wherein said diaphragm annularportion is sealed to. fixed to and bonded to said body annular surfacearound the complete circumference thereof.

12. The invention as defined in claim 4, wherein said diaphragm annularportion is sealed to. fixed to and bonded to said body annular surfacearound the com plete circumference thereof.

13. A transducer comprising: a base; a member; means mounting saidmember on said base to move in a predetermined direction in accordancewith a predetermined variable; a leafspring cantilever beam having abeam plane and a plane of symmetry normal thereto and having one fixedend and another opposite end free; a strain gage fixed to opposite sidesof said beam; means mounting said beam in a fixed position relative tosaid base and in a position approximately normal to said predetermineddirection; a stamping fixed to said member to move generally in a planenormal to both of said symmetrical and beam planes, said stamping havinga Ushaped hole punched therethrough leaving a tab which is struck outinto a plane which is generally normal to that of said stamping, saidbeam free end projecting toward said hole over and being fixed relativeto said tab; and output means connected from said strain gages toproduce an output signal of a magnitude directly proportional to saidmember movement, said tab projecting in the same direction from saidstamping as said beam projects from said fixed end thereof. said beamfree end projecting all the way through said hole. said tab and saidbeam free end having facing planar. parallel surfaces bonded together.

14. The invention as defined in claim 13, wherein said mounting meansincludes means to move said member in a manner to cause said beam tobend only in said predetermined direction.

1. Apparatus for connection from a source of a fluid under pressure to produce an output which is a function of the fluid pressure, said apparatus comprising: a body having a hole extending completely therethrough; a generally planar, flexible diaphragm fixed relative to said body over each end of said hole, each said diaphragm having a central portion including a circular embossment outside said body having a surface the same as onehalf of a torus cut by a plane normal to its axis, each said diaphragm having an approximately uniform thickness throughout its extent, each of said diaphragm central portions also including a circular flat portion everywhere connected with said embossment inside thereof; a disc for each diaphragm of approximately the same diameter as those of the respective diaphragm flat portions and everywhere bonded thereto, each said disc having a threaded stud on the same axis; a post threaded at its opposite ends to said studs, respectively, said post being fixed relative to both of said studs; input means for supplying fluids to one side of each of said diaphragms outside said body, said fluids being under different pressures; and output means connected between said post and said body to produce an output which is a function of the difference between the pressures of said fluids.
 2. A transducer comprising: a base; a member; means mounting said member on said base to move in a predetermined direction in accordance with a predetermined variable; a leaf spring cantilever beam having a beam plane and a plane of symmetry normal thereto and having one fixed end and another opposite end free; a strain gage fixed to opposite sides of said beam; means mounting said beam in a fixed position relative to said base and in a position approximately normal to said predetermined direction; a stamping fixed to said member to move generally in a plane normal to both of said symmetrical and beam planes, said stamping having a U-shaped hole punched therethrough leaving a tab thin in comparison to its length which is struck out into a plane which is generally normal to that of said stamping, said beam free end projecting toward said hole over and being fixed relative to said tab in a position spaced from said stamping plane; and output means connected from said strain gages to produce an output signal of a magnitude directly proportional to said member movement.
 3. The invention as defined in claim 2, wherein said mounting means includes means to move said member in a manner to cause said beam to bend only in said predetermined direction.
 4. Apparatus for connection from a source of a fluid under pressure to produce an output which is a function of the fluid pressure, said apparatus comprising: an annular body having a flat, annular surface between a first inner circle and a first outer circle concentric with said first inner circle; a generally planar circular diaphragm having a generally symmetrical center and an axis through said center normal to the diaphragm plane, said diaphragm also having a flat circular portion around said center and a flat annular portion at its outer edge between a second inner circle and a second outer circle concentric with said second inner circle, said diaphragm annular portion being fixed relative to said body annular surface in a position such that all of said circles are concentric with said diaphragm axis, said second outer circle having a predetermined diameter, said diaphragm having an approximately uniform thickness throughout its extent, which thickness is substantially less than said second outer circle diameter, said diaphragm having an intermediate portion connected between said circular and annular portions thereof, said diaphragm intermediate portion having a wheel-shaped embossment thereon, said wheel having a hub portion, a rim portion and a plurality of spokes, said hub portion being connected from said diaphragm circular portion to said spokes, said hub portion having a surface in the shape of one-half of a first torus cut by a plane normal to its axis, said first torus axis being congruent with said diaphragm axis, said rim portion being connected from said spokes to said diaphragm annular portion, said rim portion being spaced radially from said hub and having a surface in the shape of one-half of a second torus cut by a plane normal to its axis, said second torus axis also being congruent with said diaphragm axis, said hub portion, said rim portion and said spokes all being embossed on the same side of said diaphragm intermediate portion, said hub portion, said rim portion and said spokes all being concavo-convex and defining respective channels in the other side of said diaphragm due to the approximately uniform thickness therof, the channel of each spoke communicating with both of those of said hub and rim portions, said diaphragm intermediate portion having a flat arcuate portion filling the gap between and connected between each pair of immediately adjacent spokes and filling the gap between and connected between the respective hub and rim portions connecting each said respective pair of immediately adjacent spokes, said spokes being uniformly distributed around and projecting in radial directions from said diaphragm axis, the surface of each said flat portion on said one diaphragm side lying generally in a single plane when said diaphragm is unstressed; input means for supplying a fluid under pressure to said one side of said diaphragm; and output means including auxiliary means connected between said diaphragm circular portion and said body to produce an output which is a function of said fluid pressure.
 5. The invention as defined in claim 4, wherein each of said spokes approximately has the shape of a thin hollow half cylinder of approximately concentric internal and external surfaces which are uniform in diameter throughout the length of each respective spoke, all of said internal spoke surface diameters being the same, all of said external spoke surface diameters being the same, each half cylinder being formed by cutting a thin hollow cylinder with a plane through the cylinder axis.
 6. The invention as defined in claim 5, wherein said output means includes utilization means connected from said auxiliary means.
 7. The invention as defined in claim 6, wherein said auxiliary means produces a D.C. current directly proportional to said fluid pressure, said utilization means including a milliammeter calibrated in weight per unit area.
 8. The invention as defined in claim 7, wherein said diaphragm is made of metal, said spokes being eight in number, each immediately adjacent pair of spokes having radial axes angularly spaced apart 45.degree., said diaphragm annular portion being sealed to, fixed to and bonded to the complete circumference of said body annular surface by being seam welded thereto.
 9. The invention as defined in claim 5, wherein said diaphragm is made of metal.
 10. The invention as defined in claim 4, wherein said diaphragm is made of metal.
 11. The invention as defined in claim 5, wherein said diaphragm annular portion is sealed to, fixed to and bonded to said body annular surface around the complete circumference thereof.
 12. The invention as defined in claim 4, wherein said diaphragm annular portion is sealed to, fixed to and bonded to said body annular surface around the complete circumference thereof.
 13. A transducer comprising: a base; a member; means mounting said member on said base to move in a predetermined direction in accordance with a predetermined variable; a leaf spring cantilever beam having a beam plane and a plane of symmetry normal thereto and having one fixed end and another opposite end free; a strain gage fixed to opposite sides of said beam; means mounting said beam in a fixed position relative to said base and in a position approximately normal to said predetermined direction; a stamping fixed to said member to move generally in a plane normal to both of said symmetrical and beam planes, said stamping having a U-shaped hole punched therethrough leaving a tab which is struck out into a plane which is generally normal to that of said stamping, said beam free end projecting toward said hole over and being fixed relative to said tab; and output means connected from said strain gages to produce an output signal of a magnitude directly proportional to said member movement, said tab projecting in the same direction from said stamping as said beam projects from said fixed end thereof, said beam free end projecting all the way through said hole, said tab and said beam free end having facing planar, parallel surfaces bonded together.
 14. The invention as defined in claim 13, wherein said mounting means includes means to move said member in a manner to cause said beam to bend only in said predetermined direction. 